This group of 4 investigators continues to use biochemical and somatic cell genetic tools to investigate immunologic mechanisms. Homogeneous cell lines have been developed and are used in many of the studies described. Significant progress has been made in understanding the antigenic determinants which T cells recognize on target cells, in the role of imunologic mechanisms in leprosy and other parasitic diseases, in the bicochemical mechanisms of macrophage function, and in the genetic control of immunoglobulin production.